VS2008 will only show the Config manager if the solution node is visible in the Solution Explorer.
If you only have a single project, the solution will not show hence you can't see the config manager.
To solve this, make sure the following option is checked.
Tools|Options|Projects and Solutions|General|Always Show Solution
This user took this information from DaveL's answer to this
] question in StackOverflow. Full credit goes to the problem solver on Stack Overflow.
Edited by Peter O'Hanlon in response to comment about poster plagiarising work.